This invention relates to electrical test apparatus, and more particularly to a low cost indicator of excessive temperature at the terminals of an electrical device.
Most items of electrical apparatus intended for operation from commercial power sources characteristically employ terminations for the wiring that supply them with power. For proper and safe operation, these items of electrical apparatus must be wired correctly at their terminations. An improperly terminated conductor, whether the termination be the contacting blade surfaces of a plug-in type connection or a terminal contacting a stranded or solid conductor, may overheat at such termination when carrying current, bringing with it the hazard of damaging any combustible material that may happen to be in contact with the overheated terminal. If detected early, however, this hazard can be overcome by correcting the wiring which brought it about. Therefore, it would be desirable to provide a simple, low cost temperature sensor that can reliably provide a warning of potential hazard due to electrical wiring overheating. In the event the terminations which might be subject to overheating are located within a junction box housing a duplex receptacle, it would be convenient to employ such sensor in a form which readily lends itself to being plugged into the receptacle. Alternatively, if the terminations to be monitored are located in a cube tap, the sensor may conveniently be built into the tap as an integral portion thereof.
Indicator devices are disclosed and claimed in Kornrumpf et al.--U.S. Pat. No. 4,310,837, issued Jan. 12, 1982, and assigned to the instant assignee. However, for the devices shown in U.S. Pat. No. 4,310,837, the temperature sensor (e.g. thermistor) relies on the material composition of the prongs to couple heat from the electrical termination to the sensor and with respect to the terminations the sensor is located at the distal end of the prong. This causes a lag between changes in temperature at the termination and the instant they are detected by the sensor. Further, the devices of U.S. Pat. No. 4,310,837 use current supplied to the electrical termination being monitored to provide an indication of overheating, thereby increasing heating of the termination.
Additionally, no means is disclosed in U.S. Pat. No. 4,310,837 to provide a quantitative indication of the temperature of the electrical termination. A temperature rise at an electrical termination caused by electrical losses and sufficient to issue an excessive temperature warning by devices of U.S. Pat. No. 4,310,837 may not occur until a substantial current flows through the termination. By monitoring the actual temperature rise of an electrical termination and the amount of current supplied thereby, the adequacy of termination wiring based on predetermined safe temperature rise limits for a known current may be determined without disassembling hardware to gain access to the termination.
Accordingly, an object of the present invention is to provide low cost apparatus for sensing overheating of current-carrying electrical conductors wherein a quantitative indication of a temperature of the conductors is provided.
Another object is to provide apparatus for reliably identifying improper termination of electrical conductors without need for line voltage power.
Another object is to provide a cube tap which signals an indication of overheating therein.
Another object is to provide a plug-in type device for sensing overheating of a duplex receptacle wherein the sensing means is in close proximity to the terminals.